Method and system for frequencymodulating stabilized oscillators



4 Sheets-Sheet l uw k L. E. NORTON w LWMTN STABILIZED OSCILLJTORS` lNVENTOR ATTORNEY m E* M METHOD AND SYSTEM FOR FREQUENCY-MODULATING NNW March 10, 1953 Filed Sept. 14, 1949 Q M w H 4 Sheets-Sheet 2 L. E. NORTON STABILIZED OSCILLATORS INVENTOR El/rbn. L

ATTORNEY Zowll f METHOD AND SYSTEM FOR FREQUENCY-MODULATING .w w IMHR.

March 10, 1953 Filed Sept. 14, 1949 March l0, 1953 l.. E. NoRToN 2,631,269

METHOD AND SYSTEM FOR FREQUENCY-MODULATING STABILIZED OSCILLATORS Filed Sept. 14, 1949 4 Sheets-Sheet 5 i INVENTOR t M25/51g ATTO RN EY March 10, 1953 L. E. NORTON 2,531,269

METHOD AND SYSTEM FOR FREQUENCY-MODULATING STABILIZED OSCILLATORS Filed sept. 14, 1949 4 Sheets-Sheet 4 n .w mM. w L.. A" .WQNN |H| mm mmkm M Jl w oy/l Y J uw Kmwkk .n wm S m@ S N. .w F I* L.. R I u M Patented Mar. 10, 1953 METHOD Aun SYSTEM Fon FREQUENCYf noouaarlrio STABILIZED osoitteroas.

Lowell E. Norton, Princeton, N. Je., assignerv to- Radio Corporation of America., a corporation of Delaware Application ,September 14, 1949 ,Serial N o, 1.1.5,69

19 Claims. 1L

This invention relates to methods, and, systeme for freouenoyfrnodillatioe an oscillator. partier- 1ar1y a microwave osoillator Whose mean oarrier frequency is stabilized lo frequency-stabilizing systems aaa methods such as disclosed in vcopending applications Serial No.1 4.49)?, led J anuary 2,7, 19.48;'Se1ia1 No- 35,1s5, sied June25, 194s', Patent No. aill, granted February 5 195,2; Serial No. 49,9734, iiled June 30. 419t?, Patent No. 2,602,897. granted July 8, 1952,; Serial No. 5,563, filed January 31 1948; lSerial No. 29,836, led May 28, 1948 (abandoned, Serial No. 236,945, filed `July 16, 1951, is a C011- tinuation thereof) Serial No. 51,253, illed September 25, 1948, Patent No. 2,559,719, granted July 10, 1951; Serial No. 53,295, led November 4, 1948; Serial No. 58,296, filed Noyember 4, V19.48, Patent No. 2,555,131, granted May 29, 1951; Serial No. 68,643, filed December 31, 1948; and Serial No. 73,626, filed January 29, 19.49, there are produced two series. of pulses, one series containing frequency-error information, and the other series containing standard=frequency information, whose time or. phase relation is, compared, as bya phase or coincidence, detector. for determination of the. frequency of an oscillator from its desired Value. The frequency. of the oscillator is automatically controlled, :as by the output of the phase detector, to. min-imize'deviation from a predetermined time. or phase. relation of the pulses of therespective. series which corresponds With the @esiefl @Scillzt ffequncyi,

In accordance with. the present invention, the stabilized oscillatorv is frequency modulated, as

at audio or video frequenties. 'by delaying the f pulses of at least one of the aforesaid series in accordance with the modulation; preferably, the pulses of the respective series are differentially delayed both substantiallyto increase the modulation factor and to reduce hum or noise.

More specifically, some yforms of the invention, the pulse-delay network comprises a pulse generator, such as a multi-Vibrator, phantastron or the like, which is triggered by the frequency-.errory or standard-frequency pulses of constant repetition rate and the modulationis utilized to determine, directly or indirectly, the timing or the corresponding output pulses, the interval between successive output pulses varying with the modulation. v*Ir-L1, other modifications of the invention, the frequency-errorl or standardfrequency pulses are applied to a delay line having a suitable number.' of reactance-resistance sections whose delay characteristics is varied in aooordaiiee Willitlie, modulation by' applying the modulating potential to one or more electronic tubes Vutilized as reactors er resistors of the delay line.'V all'forms oi the invention, the phase or time relation' between the two series of pulses is determined jointly bythe modulation and by drift of the "oscillator frequency-trom its desired value. The ipulse repetitien rate is highv compared to the` highest modulating-frequency so that the control 'off the mean carrier frequency is rigid despite modulation and se that the stabiliaioe oulses. lllav be iillereo. out alld'llol alf?- pear as al modulation component.

The invention further resides in methods and systems having novelV aduseful `features. hereinafter described. and; claimed.

For Afurther understanding or the invention and for illustratien of' embodiments thereof, reference is made to the aceompanying drawings in which;

Fig, 1 is a blolg diagramr of a frequencymodulated, frequency-stabilized oscillator system;

Fig, 2 is anexplanatory iigurereferred to in disoussioii of the ooeiailoll of Fieli s Figs. 3, 4, 5, and 6 4se hematically illustrate various pulse-delay networks and associated compo- .merits utilizable .irl the syste@ of, Figlf Referring, to Fia 1 the lolooli lll is generically illustrative of a frequency-controlled"oscillator, particularly a magnetron, klystron or other m-icrowave generator.' .for supplying ciali-frequency energy to a ,load lly throats suitable iiailsmlssion line ll, The load' ll .may be ail aliieiiiia system, a power amplifier or the atteiillator liet- Work of a signal 'eiieratos Tile blool; .Il is eeoerioally illustrative of a4 search oscillator Whose fieoiienoy .is repeatedly swept over a range of frequencies, as by a' mechanical or electronic modulating means 110t- Tlle fang@ 0l fle' quencies swept by oscillator I3r includes the resonant frequency Qf l l'lfh,v .Q $15,999.91@ l5., Which for microwave frequen sieY is` preferably section of waveguide .or resonant oai/ity containing `sas exhibiting molecular resonance! The transmission line .le which. trails s .enerev iioiii the oscillator i3 to the gas orequiyalent, may, rlike transmission line' t2 .be a waveguide, a ooo- .oeiitric line, or other transmission lille, "suitable for transmission at the fr u oies involved!w High-frequency .energy ail ofiia'ed by or through the ses cell L5, oi esuli/aient is im- Pressed nooo a il-emosllilaior le; suoli .as aioe or crystal rectiner, to ,reduce av series 0f DlllSeS eaoli ooooiiirls as the ireo ,off soillator' 'll sweees thioiieil the. resonant .freenet of the standard '.5- "Fliese sulses.aafter low/,g .ampliarse 3 and shaped by the networks l'l and I8, are applied to one input circuit of a phase detector I9 to serve as a frequency/time standard.

The outputs of the oscillators SG and i3 are in part impressed through directional couplers 2|, 2| or the like upon a mixer 26, which may be a crystal rectifier, so to produce a varying beat-frequency corresponding, for example, with the difference-frequency of the two oscillators. This varying beat-frequency is converted, as by a frequency-selective network 22 and dernodulator 23, into a second series of pulses each occurring as the beat-frequency passes through a predetermined fixed value. As discussed in the' aforesaid applications, this fixed frequency may be the pass frequency of a beat-frequency amplier, the cutoff frequency of a lter, or the null-output frequency of a discriminator. In all cases, this second series; of pulses contains frequency error/time information corresponding with the deviation of the carrier frequency of oscillator l from its desired value. This second series of pulses, after amplification and -shaping by the networks 24 and 25, is applied to a second input circuit of the phase detector i9. The unidirectional output voltage of the to vary the potential of the reflector anode;

when the oscillator tube is a magnetron, the control voltage may be applied to a frequencycontrol electrode within the tube, as disclosed in certain of the aforesaid applications, or to a frequency-controlled tube associated therewith; for lower-frequency oscillators, the control-voltage output of phase detector i9 may be applied in known manner to a reactance tube controlling the oscillator frequency.

As thus far described, the system of Fig. l is for rigidly stabilizing the frequency of oscillator l0 in manner generic to the various methods and systems of the aforesaid copending applications. In all of them, any departure from a predetermined time or phase relation of the two series of pulses applied to phase detector I9 produces changes in the output Voltage of the detector which is representative of deviation of oscillator l0 from its desired value and which is applied in correction for such deviation.

In accordance with the present invention, the phase relation between the two series of pulses is also varied in accordance with the desired modulation, at audio or Video frequencies, so to effect frequency-modulation of the output of oscillator I0. To that end, the pulses of one or both series are delayed in accordance with the modulation; when both series of pulses are variably delayed, they are delayed differentially, as later more fully described.

As shown in Fig. 1, a vdelay network 2 may be included in circuit between the demodulator 23 and the phase detector I9, as by a switch 28a which also couples the delay network to a modulator 29. Thus in their passage from the demodulator 23 to the phase detector I9, the frequency-error pulses are subject to a variable delay corresponding with the applied modulation, and the time or phase relation between the two series of pulses, as compared by phase detector I9, will therefore Vary with the modulation and correspondingly vary the unidirectional output yoltage of the phase detector. This causes the instantaneous frequency of the oscillator Ill to vary with the modulation. The delay network 2l preferably has a linear characteristic D, Fig. 2, so that the delay introduced is proportional to the amplitude of the modulating signal. The delay corresponding with zero modulation is at an operating point O intermediate or substantially midway the limits of the characteristic D so that the delay time increases and decreases in accordance with the modulating signal S, the magnitude of the increase and decrease depending, as aforesaid, upon the amplitude of the modulating signal. As evident fromv Fig. 2, for signals S1 of low amplitude, the range of the time delay is substantially smaller than for signals S2 of larger amplitude because the'conden-ser 33 charges up to a higher value for the larger signals. As the repetition rate of the pulses is high compared to the frequency of the modulation, each wave of the modulation corresponds with many pulses, and these are each advanced or retarded in time in accordance with the amplitude and polarity of the instantaneous Values of the signal during its cycle.

Alternatively, or in addition, a similar delay network 2l may be interposed, as by switch 28h, in circuit between the demodulator I6 and the phase detector I9 to shift the standard-frequency pulses in accordance with the modulation. When, and as preferably, both delay networks 21 are included, the modulation is applied to them differentially, as by transformer 3i! so that the modulating voltages are applied to `the delay networks out-of-phase, as indicated by the dotted and full line waves Si and S2 of Fig. 2. Accordingly, as the modulation is applied to one delay network to decrease the time delay of pulses passing through it, the l iodulation potential concurrently applied to the other delay network increases the delay suffered by the other series of pulses. Thus, the shift in phase relation between the two series of pulses which is due to modulation, is effectively doubled as detected by the phase comparator I9. By differentially delaying the pulses in accordance with modulation, the modulation factor in the system is substantially increased and any hum or noise is substantially balanced out when, as preferable, the two delay networks are of substantially similar composition. As the repetition rate of the pulses is substantially higher than the highest modulating frequency, the pulse frequency may be readily highly attenuated to eliminate it as a modulation component of the output voltage of i9.

In the particular form of delay network shown in Fig. 3, the standard-frequency pulses or the frequency-error pulses are applied to one grid of tube 3i and the modulation signal is applied to another grid of that tube. Accordingly, the output of tube 3l is a series of pulses having the same repetition rate as the sweep frequency of oscillator I3 and whose peak values vary in accordance with the modulating sig-nal. These amplitude-modulated pulses are applied as triggering pulses for a multi-vibrator network 27a including the tubes 32 and 33 whose grids and anodes are cross-connected by coupling condensers 3d, 3d. In the interval between successive pulses, the tube 32 is conducting whereas tube 33 is nonconducting because biased to or beyond cutoff j by the resistancefcapacitance network 35-36. when a negative pulse is applied to th-e grid of tube SZ, its anode current is out off and the pulse as applied to tube 33 causes it to conduct. rIhe condenser 33 in the grid circuit of tube 32 is charged to a potential closely approximating the peak'value of the negative pulse. The voltage across condenser 'S8 then gradually decreases by discharge through resistor 3l until a critical value is reached, at which time tube 32 again conducts and tube 33 is again c ut oi. This sequence of operations is repeated for each successive pulse 'from tube 3|. The periods during which tube 32 conducts can be .made to vary substantially linearly with the peak Values of the pulses from tube 3l by providing that the time constant of the network lfs'shall be large compared to the repetition period of the pulses. The output of the multivibrator therefore consists of a series of square-.wave pulses having the same repetition rate as the search oscillator I3, the duration of the pulses varying with the signal from modulator 29. These square-wave pulses are dinerentiated by a condenserfresistance networkdI-llz to provide positive and negative pulses corre-- spending with initiation and termination of the square-wave output pulses of the multi-vibrator. In the particular arrangement disclosed, the diode d3 effectively removes the positive pulses leaving a series of negative pulses of the same repetition frequency as search oscillator i3 but with the interval between successive pulses varying `as a linear function of the modulating signal.

In other words, the pulses across the resistor d2 correspond with the pulses from demodulator I6 or 23, each delayed, however, in accordance with the instantaneous amplitude of the modulating signal. These pulses are converted by a shaping network Ia to sawtooth Waves of the same repetition frequency as the search oscilla-` work including two pairs of rectiers lll of diode'- or crystal type.

When, as shown in Fig. 3, the modulation is applied variably to delay both the `frequencyerror pulses and the standard-frequency pulses,

the modulating signal may be applied to a tube" il having load resistances 4S and 5K3 respectively in the anode and cathode circuits to afford pushpull output. The modulating-voltage appearing across the load resistor 4'9 is impressed, as above described, upon the tube 3.! of one of the delay networks NA, and the modulating signal across cathode resistor 50 is applied to the corresponding tube of a second similar delay network 21A upon which is impressed the pulses from the de-a.

Thus, the Standard-frequency modulator i5. y pulses are also delayed in accordance with the modulation, and after shaping by the network 25 including tube 5d, condenser 5l and resistor 52 are impressed upon the second input circuitv of' j lthe phase comparator 19a.

There is thusrroduced across the Output terminals 0f the phase-detector ISA a unidirectional voltage which varies not only with the devia- A tions from normal of the frequency of oscillatorv '-Hl, but 'also accordance With'the modulating signal. In-the particular circuit shown in Fig. 3, the frequency-control voltagefproduced by comparator ld is applied to the 'grid of a frequencycontrol tube 55 for a reflex klystron IDA. The an.- ode-cathode resistance of tube 55, as affected by the potential of its control grid, determines the potential of the reflex-anode ofthe klystron IA and therefore determines the output frequency of the klystron. The klystron may be set approximately to its desired operating -irequency by adjustment of the dimensions of its cavity, as understood by those skilled inthe art, and may be more closely adjusted to proper frequency by adjustment of the xed component of thepotential of the'control grid of tube 55; specifically, the grid circuit of tube may include a potentiometer 58 and battery 5l for the latter purpose. The grid potential of tube v55 is determined both by the setting of potentiometer 5S and by the output voltage ofthe phase detector ld, which as appearing across condenser 53, includes both frequency-corjrective andI frequency-modulating components.

in the modicatien shown in Fig. 4, the delay network 21B for use in the system of Fig. 1 comprises one form of the so-called phantastron circuit.y For other forms thereof and for del scription oi their operation, reference is made to the Design of phantastron time delay circuits appearing in thefApril 1,948, issue of "lillectronicsfy In the form show-n, frequency-error pulses, or the standard frequency pulses, are applied to the #3 grid of tube te, which may be of the GSA'? type. This grid is at positive potential with respect to ground, this operating potential being determined by the relative magnitudes of theAvoltagedividing resistors (i I and 62; the #2 and #4 grids of thisI` tube are also of positive potential with respect to groundthe magnitude of this operating potential being determined byA the relative magnitudes o f resistors 63- andll, rWhen a pulse is applied, the time at which the corresponding pulses appear across the cathode resistor 58 depends upon the instantaneous` potentia1 of the #l grid as determined by resistor 65, condenser (il and cathode 'resistor S8 of an associated triode 66. `Variably to delay the '91119D1113 pulses in accordance with the modulation, the modulating signal is applied to the grid of tube 48A whose anode 4is coupled to the `grid of tube 66 and to the anode of` tube BQ by a diode 63. Actually, the triade' te and diode 'es may be @ne two halves of a GSNT tube, the plate and gridof one section being connected together to`r serve as a diode. The operation of the fphantastron circuit per se is quite complicated, and being vf ully discussed in the aforesaid issue of Electronicsf is not in detail described here. It suiiices here to say that the output pulses of `the delay network 21B correspond in number with the input pulses from deinodu'lator I6 or 23, Fig. l, with the time interval between successive output pulses varying in accordance with the modulating voltage. The output'pulses of network 21B are shaped by networks 25a or 18a and impressed upon a phase discriminator which maybe of-anysuitable type; in the -forrn shown, phase discriminator moisA of the type more fully disclosed in aforesaid copending applications serial Nos. 4,4 97 and 29,836. 'The instantaneous magnitude of the output voltage ofthe phase comparator follows the modulating signal and accordingly varies the frequency of oscillator |0A. The average magnitude ofthe output voltage of the phase'comparator in this, asin all other inodiflcationavaries with deviation "of the mean-carrier frequencyof the oscillator from its desired value and is accordingly effective to correct such deviation.

In the modification shown in Fig. 5, the delay lnetwork 21C interposed in either or both of the input circuits of the phase comparator I9 comprises a delay line having a suitable number of sections each including a series inductance 10 and a shunt capacitance 1l. To vary the delay of the standard-frequency or frequency-error pulses, the effective shunt capacitance of a suitable number of sections of the delay line is varied in accordance with the modulation. Specifically,A eachof one or more of the condensers 12 is shunted .by a reactanc'e tube network 'l2 which ,exhibits capacitive reactance of magnitude determined by the potential of the grid of tube 13 of the network. Specifically, the tube 'I3 is a pentode, such as a 6VSJ7 or 6AC7 type of tube having its grid coupled toa point between resistance i4 and condenser 'l5 in parallel to condenser 'll and to the anode-cathode circuit of the tube. As the operating principles of a rev actance tube are Well understood by those skilled Vin the art, further description of network 12 is unnecessary here. `It suflices to say that the frequency-error or standard-frequency pulses applied to the input terminals of the line 21C appear across the output terminals thereof with delay varying linearly as a function of the modulating signal applied to tube or tubes 13. These delayed pulses are impressed upon the phase comparator I9 and accordingly the unidirectional output voltage of the phase comparator, applied to the oscillator lll for control of its frequency, varies in accordance with the modulation.

In the modification shown in Fig. 6, the delay network 21D for variably delaying the standard frequency pulses and/or the frequency error pulses of Fig. Vl comprises a delay line of suitable number of sections including series inductance L modified. by variable resistance 80, and shunt capacitance 8|. Each of one or more series resistances of the line is the cathode-anode resistance of a tube 80 whose grid potential is varied in accordance with the modulation. The choke 83 in the anode current supply circuit of the tube is of high impedance to the pulses. Accordingly, the frequency-stabilizing pulses applied to the input terminals of the line 21D appear at the output terminals thereof with timespacing whichfollows the modulation and therefore the instantaneous frequency of the oscillator is varied in accordance with the modulation, the mean carrier frequency of the oscillator, however, being rigidly stabilized as in the aforesaid copending applications.

From the foregoing explanation, it shall be understood the invention is not limited to the specic arrangements described but that changes and modifications may be made within the scope of the appended claims.

What is claimed is:

l. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises generating search oscillations, repeatedly sweeping the frequency of said .search oscillations over a range including a standard frequency to produce a series of pulses, producing a second series of pulses each occurring as the beat frequency of the oscillator frequency and said search oscillations passes through a predetermined value, delaying the pulses of at least one of said series in accordance with the desiredV lllodulation.` andvarying .the frequency of the oscillator in accordance with sense and magnitude of the variations in the time relation between the pulses of the two series as affected both by the modulation and by drift of the mean carrier frequency. v

2. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises generating search oscillations, repeatedly sweeping the frequency of said search oscillations over a range including a standard frequency to produce a series of pulses, producing a second series of pulses each occurring as the beat frequency of the oscillator frequency and said search oscillations passes through a predetermined value, differentially delaying' the corresponding pulses of the respective series in accordance with the desired modulation, rand varying the frequency of the oscillator in accordance with sense and magnitude of the variations in the time relation between the pulses of the two series as affected both by the modulation and by drift of the mean carrier frequency.

3. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises generating search oscillations, repeatedly sweeping the frequency of said search oscillations over a range including a standard frequency to produce a series of pulses, producing a second series of pulses each occurring as the beat frequency of the oscillator frequency and said search oscillations passes through a predetermined value, delaying the pulses of one of said series in accordance with the desired modulation, and varying the frequency of the oscillator in accordance with sense and magnitude of the variations in the time relation between the pulses of the two series as affected both by the modulation and by drift of the mean carrier frequency.

4. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing a series of pulses containing frequency error information, producing a second series of pulses containing frequency error information, producing a second series of pulses containing standard frequency information, delaying the pulses of at least one of said series in accordance with the desired modulation, and varying the frequency of the oscillator in accordance with variations of the time relation between the pulses of the two series as affected both by the desired modulation and by any drift of the mean carrier frequency.

, 5. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing a series of pulses containing frequency error information, producing a second series of pulses containing standard frequency information, differentially delaying the pulses of the respective series in accordance with the desired modulation, and varyingy the frequency of the oscillator in accordance with variations of the time relation between the pulses of the Ytwo series as affected both by the desired modulation and by any drift of the mean carrier frequency.

ulation` whereby the; 'phase relation between che twoI series, oi pulses is dependent both uponthe modulation and upon the frequency error ofr the oscillator, and applying to, the oscillator' a frequency-control signal of magnitude varying with variations: of said phaserelation.

7. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing a series or" pulses containing frequency error information, producing a second series` of pulses containing standard-frequency information, delaying the pulsesl of at least one of said series,` varying said delay characteristics iny accordance withv a modulating signal, comparing the phase relation ofthe pulses of' the respective series as affected both by frequency error of the oscillator andl by the modulating signaL and applying tov the oscillator a frequency-control signal ofl magnitude varying with variations of the compared phase relation of the pulses. 8. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing a series of pulses containing Ifrequency error information, producing a second seriesl of pulses containing standard frequency information, delaying the pulses of at least one of said series, varying said delay characteristic in accordance with a modulatingsignal, comparing'the phase relation of the respective series as affected both by frequency error of the oscillator and by the modulating signal, and applying to the oscillator a frefluency-control signal of magnitude varying with variations of the compared phase-relation of the pulses. f

9. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing two series of pulses respectively containing frequency error versus time information and standard frequency versus time information, converting the pulses of each of said series to pulses of duration varying in accordance with a modulating signal, the variation being differential for pulses of the different series, differentiating the variable duration pulses to produce two series of pulses corresponding with the original series but with a differential time shift dependent upon the modulation, and applying to the oscillator a frequency-control signal of magnitude Varying with variations of the phase relation of the dierentiated pulses.

10. The method of frequency-modulating and stabilizing the mean carrier frequency of an oscillator which comprises producing two series of pulses respectively containing frequency error versus time information and standard frequency versus time information, separately delaying the two series of pulses, diiferentially varying said Idelayed series of pulses in accordance with a modulating signal, lcomparing the phase relation lof the diiferentially delayed pulses, and applying to 'the-oscillator a frequency-control signal vary- .ing in accordance with the .compared phase relation of the pulses and so containing both frequency* error Acorrective modulation components.

11. The method of utilizing resonant microwave absorption in a gas for frequency-nodulatlng and stabilizing the mean carrier frequency of an oscillator which comprises generating variable frequency microwave oscillations, repeatedly sweeping the frequency of said microwave oscillations over a range including the molecular resonant frequency .of .a gas, applying said oscillations to said ses. deriving a series of pulsescouteiuiue standard frequency versus time information. 1.1.1 responsey to said gas resonantabsorption, producing a second series' of pulses; each occurring as the beat frequency of the oscillator and said. swept oscillations passes through a predetermined freequency so to contain frequency error versus, time information, shifting the phase relation between the two series of pulsesy in accordance with the desired modulation, comparing the phase, relation of the pulses of the respective series as aected both by the modulation and by deviation of the mean carrier frequency of said' oscillator, and applying to said.A oscillator a frequency-control signal varying with variations of the compared phase relation of said pulses.

12.., A frequency-modulated, frequency-,stabilized oscillator system comprising an oscillator, a high, precision` frequency Standard, o Search oscillator for repeatedly sweep-ius o reuse iuoludine the resonant frequency of seid. standard a demodulator for producing a series of: pulsos each occurring as the Search oscillator frequency sweeps the resonant frequency of said. standard, means including a miser and o frequency-.selec tive network for producing a series of pulses, esclu occurring as the beatireouency of. said oscillators sweeps e predeterm'ued frequency@ phase detector hav-ing input circuits upon which said two series oi pulses are respectively impressed for producins a unidirectional .cutout voltage varying iu accordance with variations in the phase relation of the pulses of the respective series, delay means in at leest one of said inout circuits, modulating means for varying the delay characteristic of said delay means so to vary the phase relation between pulses of the respective series in accordance. rwith the modulation. and mea-us for applying seid out.- cut voltage to stabilize the mee-u frequency ol? the lust-named oscillator and to vary .the instanten necus frequency thereof in accordance with the modulation.

13. A frequency-modulated, frequency-stabi.-

lzed oscillator system comprising an oscillator, a high precision frequency standard, a Search oscillator for repeatedly sweeping a range includine the resonant frequency of said standard. a demodulator for producing a. series of pulses each occurring as the .Search oscillator frequency sweeps the. resonant ifredueucy oi said standard. means including mixer `and a freducucysselccf tive network for producing a series of pulses each occurring as the bea-t frequency of said oscillators `sweeps a predetermined frequency. a phase detecf vor having input circuits upon Which, said two series oi pulses are resuectiveiy impressed for produelos o uu eeuoual output voltage var-ying in accordenc` Y. l1 variations the phase relation of the pulses of the respective series, delay means in each of said input circuits, modulating means for differentially varying thedelay.characteristics of said .delay means so to `vary the phase relation between pulses of the respective series in accordance with the modulation, and means for applying said output voltage to stabilize fthe mean fre.- ;duency ,ci the nrstfnamed Losciliator and to yary the instantaneous frequency thereof in accordance with the modulation.

14. A frequency-modulated, frequency-stabilized oscillator system comprising an oscillator, means for producing a series of pulses containing frequency error information, means for producing a second series of pulses containing standard frequency information, a phase detector having input circuits upon which said pulses are respectively impressed for production of a unidirectional output voltage varying in accordance with variations in the phase relation of the pulses of the respective series, delay means in at least one of said input circuits, modulating means for varying the delay characteristics of said delay means so to vary the phase relation between pulses of the respective series in accordance with the modulation, and means for applying said unidirectional output voltage to stabilize the mean carrier frequency of the oscillator and to vary its instantaneous frequency in accordance with the modulation.

15. A frequency-modulated, frequency-stabilized oscillator system comprising an oscillator, means for producing a series of pulses containing frequency-error information, means for producing a second series of pulses containing standard-frequency information, a phase detector having input circuits upon which said pulses are respectively impressed for production of a unidirectional output voltage varying in accordance with variations in the phase relation of the pulses of the respective series, a time-delay network in each of said input circuits, modulating means for differentially varying the delay characteristics of said delay networks, and means for applying said output voltage to stabilize the mean frequency of the oscillator and to vary its instantaneous frequency in accordance with the modulation.

16. A frequency-modulated, frequency-stabilized oscillator system comprising an oscillator, means for stabilizing the mean carrier frequency of said oscillator comprising means for producing two series of pulses respectively containing standard-frequency versus time information and frequency-error versus time information, andra phase comparator having input circuits upon which said series of pulses are respectively impressed and producing a frequency control for said oscillator of magnitude varying with variation of the time relation of the pulses of the respective series, and means for frequency-modulating said oscillator comprising a pulse generator interposed in at least one of said input circuits for triggering by the corresponding series of aforesaid pulses to produce a corresponding number of output pulses for application to said phase comparator, and means for applying a modulating signal to said pulse generator variably to delay said output pulses in accordance with the modulation. Y

17. A frequency-modulated, frequency-stabilized oscillator system comprising an oscillator, means for stabilizing the carrier frequency of said oscillator comprising means for producing two series of pulses respectively containing standard-frequency versus time information and frequency-error versus time information, and a phase comparator having input circuits upon which said series of pulses are respectively impressed and producing a frequency control for said oscillator of magnitude varying with variation of the time relation of the pulses of the Vrespective series, and means for frequency-modulating said oscillator comprising pulse generators interposed in said respective input circuits re'- spectively for triggering by said two series of pulses, each to produce output pulses of the same repetition rate, and means for applying a modulating signal to said pulse generators differentially and variably to delay said output pulses in ac cordance with the modulation.

18. A frequency-modulated, frequency-Stabid lized oscillator system comprising an oscillator, means for stabilizing the mean carrier frequency of said oscillator comprising means for producing two series of pulses respectively containing standard-frequency versus time information and frequency-error versus time information, and a phase comparator having input circuits upon which said series of pulses are respectively impressed and producing a frequency control for said oscillator of magnitude varying with variation of the time relation of the pulses of the ref spective series, and means for frequency-modulating said oscillator comprising a delay line interposed in one of said input circuits and having series and parallel impedances, at least one of which is an electronic tube, and means for applying a modulating signal to said tube variably to delay the transmission of pulses by'said line to said comparator in accordance with the modulation.

19. A frequency-modulated, frequency-stabilized oscillator system comprising an oscillator, means for stabilizing the mean carrier frequency of said oscillator comprising means for producing two series of pulses respectively containing standard-frequency versus time information and frequency-error versus time information, and a phase comparator having input circuits upon which said series of pulses are respectively impressed and producing afrequency control for said oscillator of magnitude varying with varia-I tion of the time relation of the pulses of the respectivel series, and means for frequency-modulating said oscillator comprising delay lines respectively interposed in said input circuits and each having series and parallel impedances, at least one of which is an electronic tube, and means for applying a modulating signal to said tubes differentially and variably to delay the transmission of pulses by said lines to said comparator in accordance with the modulation.

LOWELL E. NORTON.

' REFERENCES CITED f The .following references are of record in the file of this patent:

UNrrED STATES PATENTS 

